From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756323AbeATR5C (ORCPT ); Sat, 20 Jan 2018 12:57:02 -0500 Received: from mail-pg0-f65.google.com ([74.125.83.65]:33768 "EHLO mail-pg0-f65.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755008AbeATR4w (ORCPT ); Sat, 20 Jan 2018 12:56:52 -0500 X-Google-Smtp-Source: AH8x224WZLGETVs31vNmcfkwUVJzwrGGzK2CJVipfm8XYHkZGet+N5yxetV5S2wTCIdtInrJ8fD+9A== Subject: Re: [PATCH v2 3/8] watchdog: JZ4740: Register a restart handler To: PrasannaKumar Muralidharan Cc: Paul Cercueil , Ralf Baechle , Rob Herring , Mark Rutland , Wim Van Sebroeck , "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" , Linux-MIPS , open list , linux-watchdog@vger.kernel.org References: <20171228162939.3928-2-paul@crapouillou.net> <20171230135108.6834-1-paul@crapouillou.net> <20171230135108.6834-3-paul@crapouillou.net> <20061de8-fa1f-93eb-eb9b-089c699018aa@roeck-us.net> From: Guenter Roeck Message-ID: Date: Sat, 20 Jan 2018 09:56:48 -0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.5.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 01/20/2018 08:04 AM, PrasannaKumar Muralidharan wrote: > Hi Guenter, > > On 20 January 2018 at 21:15, Guenter Roeck wrote: >> On 01/19/2018 11:31 PM, PrasannaKumar Muralidharan wrote: >>> >>> Hi Paul, >>> >>> On 30 December 2017 at 19:21, Paul Cercueil wrote: >>>> >>>> The watchdog driver can restart the system by simply configuring the >>>> hardware for a timeout of 0 seconds. >>>> >>>> Signed-off-by: Paul Cercueil >>>> Reviewed-by: Guenter Roeck >>>> --- >>>> drivers/watchdog/jz4740_wdt.c | 9 +++++++++ >>>> 1 file changed, 9 insertions(+) >>>> >>>> v2: No change >>>> >>>> diff --git a/drivers/watchdog/jz4740_wdt.c >>>> b/drivers/watchdog/jz4740_wdt.c >>>> index 92d6ca8ceb49..fa7f49a3212c 100644 >>>> --- a/drivers/watchdog/jz4740_wdt.c >>>> +++ b/drivers/watchdog/jz4740_wdt.c >>>> @@ -130,6 +130,14 @@ static int jz4740_wdt_stop(struct watchdog_device >>>> *wdt_dev) >>>> return 0; >>>> } >>>> >>>> +static int jz4740_wdt_restart(struct watchdog_device *wdt_dev, >>>> + unsigned long action, void *data) >>>> +{ >>>> + wdt_dev->timeout = 0; >>>> + jz4740_wdt_start(wdt_dev); >>>> + return 0; >>>> +} >>>> + >>>> static const struct watchdog_info jz4740_wdt_info = { >>>> .options = WDIOF_SETTIMEOUT | WDIOF_KEEPALIVEPING | >>>> WDIOF_MAGICCLOSE, >>>> .identity = "jz4740 Watchdog", >>>> @@ -141,6 +149,7 @@ static const struct watchdog_ops jz4740_wdt_ops = { >>>> .stop = jz4740_wdt_stop, >>>> .ping = jz4740_wdt_ping, >>>> .set_timeout = jz4740_wdt_set_timeout, >>>> + .restart = jz4740_wdt_restart, >>>> }; >>>> >>>> #ifdef CONFIG_OF >>>> -- >>>> 2.11.0 >>>> >>>> >>> >>> Noticed that min_timeout of the watchdog device is set to 1 but this >>> function calls start with timeout set to 0. Even though this works I >>> feel it is better to set min_timeout to 0. >>> >> >> No. That would be wrong. If you want to be pedantic, write a new function >> __jz4740_wdt_set_timeout(u16 clock_div, u16 timeout_value) and call it >> instead, but don't mess with min_timeout. >> >> Guenter > > What is the effect of changing min_timeout? I could see only > validation checks with it. > Let me ask you - you want to let userspace set a timeout of 0, which would effectively reboot the system through the backdoor. Why ? Guenter